The present invention relates to an unsolvated crystalline form, various solvates, and the HCl monohydrate salt of the antiviral compound 5,6-dichloro-2-(isopropylamino)-1-(β-L-ribofuranosyl)-1H-benzimidazole (also known as 1263W94; maribavir; a compound of formula (I) below), pharmaceutical formulations comprising such crystalline form, solvates and the HCl monohydrate, and their use in therapy.
5,6-dichloro-2-(isopropylamino)-1-(β-L-ribofuranosyl)-1H-benzimidazole (1263W94; maribavir) is a benzimidazole derivative useful in medical therapy. U.S. Pat. No. 6,077,832 discloses 5,6-dichloro-2-(isopropylamino)-1-(β-L-ribofuranosyl)-1H-benzimidazole and its use for the treatment or prophylaxis of viral infections such as those caused by herpes viruses. The compound as disclosed in U.S. Pat. No. 6,077,832 is an amorphous, non-crystalline material.
The structure of 5,6-dichloro-2-(isopropylamino)-1-(β-L-ribofuranosyl)-1H-benzimidazole, a compound of formula (I) is shown below:

The preparation of certain crystalline forms and solvate forms of 5,6-dichloro-2-(isopropylamino)-1-(β-L-ribofuranosyl)-1H-benzimidazole, as well as pharmaceutical formulations thereof and their use in therapy are described in U.S. Pat. Nos. 6,469,160 and 6,482,939.
Different polymorphs normally have different solubilities, different residence times in the body and different therapeutic values. In view of these differences, it is important in drug development to determine the properties, and control, to the extent possible, the presence of polymorphs in any drug product administered in crystalline form that is submitted for regulatory approval.